Vacuum pump



1966 A. A. LANDFORS 3,

VACUUM PUMP Filed Aug. 24, 1964 TO ROUGHINlG PUMP United States Patent3,278,113 VACUUM PUMP Arthur A. Landfors, Sharon, Mass., assignol" toNational Research Corporation, Cambridge, Mass, a corporation ofMassachusetts Filed Aug. 24, 1964, Ser. No. 391,575

3 Claims. (Cl. 230-101) The present invention relates to high speedvacuum pumps used in lamp evacuating machines and the like.

Many vacuum lamp exhaust machines of the rotary indexing type usemercury diffusion pumps to attain the low ultimate pressure required. Atypical machine may contain 16 stationary positions connected to variousmechanical pumps and 16 rotating pumping units which move with anintermittent motion from one stationary position to the next. Eachpumping unit consists of a lamp, connecting head, and mercury diffusionpump. The first two stations on a typical machine of 16 stations areused for rough pumping. Here the pumping unit is evacuated to a pressurebelow the forepressure tolerance of the difiusion pump. The remaining 14stations are connected to a backing manifold in which the pressure willnever rise above the forepressure tolerance. At these stations thedifiusion pump continues to pump on the lamp independently of pressurechanges in the backing manifold.

It is imperative that the pressure in the pumping unit is reduced asrapidly as possibly at the roughing station. The higher the forepressuretolerance of the pump the less time will be required at the roughingstation. A high forepressure tolerance necessitates a smallcross-section of the diffuser throat. This same small cross sectionunfortunately presents an impedance at the roughing stations.

It is therefore the object of this invention to provide a pumpingtechnique which meets these conflicting requirements of highforepressure tolerance and ease of roughmg.

The invention comprises an improved pump utilizing this technique.

Referring now to the single figure of the drawing, there is shown apreferred embodiment of the improved pump of the invention as utilizedin a conventional lamp evacuating machine.

Background The lampmachine comprises several pumps 10, each pumpconsisting of a mercury ejector pump body 12 and a foreline 14. Acondensation trap 16 is included in the foreline. These assemblies aremounted on a turntable which moves past several fixed stations A, B, C,D, E, et seq. Stations B, C and D are indicated in the drawing.

A first group of the fixed stations is connected to a high speedmechanical roughing pump. A second group of fixed stations is connectedto mechanical backing pumps. As the turntable rotates the pumps '10 pastthe first group of stations, a lamp bulb 1 8, which is to be evacuated,is secured to the inlet of pump 12. The roughing pump evacuates the bulbto a rough vacuum (on the order of less than mm. Hg) via the pump body12 and pump foreline 14. The rough pumping is accomplished in less thana minute and the turntable then moves to the stations C, D, et seq,which are connected to the backing pump system.

Each pump 10 comprises a heater 20 which continuously heats a pool ofmercury 22 in the bottom of the pump. When the pressure in the pumpfalls sufficiently low, the mercury boils and the vapors emerge from afirst stage nozzle 24 and ejector nozzle 26 as pumping jets. Thesepumping jets further reduce the pressure in the pump to a desired level(on the order of less than 5 microns). The

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operation of the pump 10 proceeds as it passes one roughing stationafter another and between stations. When the turntable makes a completecircuit back to the roughing stations, the bulb is sealed, the pump 10is air released, the bulb is removed and a new bulb is applied for roughpumping.

A typical lamp evacuation system would comprise two roughing stationsand fourteen backing pump stations. The turntable would rotate at aconstant rate with sixteen lamps being processed at once.

The problem There is a fundamental mismatch in the upper limit offorepressure tolerance of pumps 10 and the lowest pressures which can bereached on a practical basis with the backing pump system. It iscustomary to accommodate this mismatch by providing a restriction in theforeline of the vapor vacuum pump. Such a restriction appears as anarrow throat 28 in the foreline 14 of ejector pump 10. This solves theforepressure tolerance problem, but creates a problem in rough pumpingspeed. The restriction of throat 28 causes failures of the rough pumpingsystem to bring the lamp down to the desired rough vacuum.

The solution The pump is modified by the addition of a Y-form bypasspipe 50 connecting the mercury reservoir 22 with both sides of thethroat 28. During exposure to pressures above the rough vacuum pressure,the mercury level in the reservoir is as indicated at 32 and the mercurylevel in the Y-form pipe 30 is as indicated at 34. The pipe 30 thenserves as a high conductance bypass for rough pumping.

As the pressure is reduced and the mercury boils in the pump anddischarges vapors through the restricted jet openings 24 and 26, gaspressure builds up over the reservoir 22 to force its level down to theline indicated by arrows 132. The bypass pipe is sized so that the levelof mercury is thereby forced up to the line indicated by dashed lines134. This cuts oif the bypass and the pump is then matched to the roughpumping system via restricted throat 28.

Thus the pump as modified is able to meet the dual requirements ofmatching forepressure tolerance to backing capabilities and highroughing speeds. This is done without the addition of expensivemechanical valves or seals. The bypass 30 has the further advantage ofaiding the return of mercury condensed in foreline 1 4 back to thereservoir 22.

Another restriction in the foreline is that caused by the ejector nozzle26, as indicated at 36. This restriction is only a minor difficultycompared to that imposed by throat 28. But restriction 36 can also bebypassed during roughing by suitable arrangement of pipe '30 as shown inthe drawing.

While one specific embodiment has been described, it should beunderstood that several variations are possible. For instance, theconnection of the bypass pump to the pump body '12 or foreline 14 can bemade at any point which is accessible to the bulb 18 via a highconductance gas path. The principles of the invention could be appliedto improve other types of vapor vacuum pumps and the improved pumps canbe utilized in many applications, other than lamp evacuating machines,requiring high speeds. It is therefore intended that the abovedescription and accompanying drawing shall be read as illustrative ofthe invention and not in a limiting sense.

What is claimed is:

1. An improved high speed vapor vacuum pump for lamp evacuating machinesand the like, comprising a pump body, heating means for vaporizing areservoir of dense working liquid, nozzle means for discharging thevapors as pumping jets, a foreline connected to the body, a restrictionin said foreline, passage means in open communication with the upstreamand downstream sides of directly into the foreline, the said pump nozzleextending into the foreline to form an annular path and wherein the saidrestriction bypass path starts from the foreline adjacent the ejectornozzle and whereby the said annular said restriction, said passage meansalso being in open 5 path is also bypassed when said bypass path isopen.

communication with said reservoir below the liquid level thereof, thepassage means being constructed to provide a bypass path around therestriction during non-boiling of the working liquid and provide aliquid seal for said bypass path during boiling of the working liquid.

2. The pump of claim 1 wherein said passage means comprise a Y-form pipewith the upper legs of the Y connected to the upstream and downstreamsides of the throat, to provide said bypass path, and the lower leg ofthe Y being connected to said reservoir to provide the source of liquidfor sealing the bypass path during boiling.

3. The pump of claim 1 wherein said pump nozzle means includes anejector nozzle for discharging a jet References Cited by the ExaminerUNITED STATES PATENTS 1,935,415 11/1933 Read Z30101 10 2,233,800 3/1941Whitney 230-401 2,797,043 6/1957 Gerow 230-401 2,806,644- 9/1957 Warren23010l 2,887,618 5/1959 Reid 260-401 15 MARK NEWMAN, Primary Examiner.

W. L FREE/H, Assistant Examiner.

1. AN IMPROVED HIGH SPEED VAPOR VACUUM PUMP FOR LAMP EVACUATING MACHINESAND THE LIKE, COMPRISING A PUMP BODY, HEATING MEANS FOR VAPORIZING ARESERVOIR OF DENSE WORKING, HEATING MEANS FOR VAPORIZING A RESERVOIR OFDENSE AS PUMPING JETS, A FORELINE CONNECTED TO THE BODY, A RESTRICTIONIN SAID FORELINE, PASSAGE MEANS IN OPEN COMMUNICATION WITH THE UPSTREAMAND DOWNSTREAM SIDES OF SAID RESTRICTION, SAID PASSAGE MEANS ALSO BEINGIN OPEN COMMUNICATION WITH SAID RESERVOIR BELOW THE LIQUID LEVELTHEREOF, THE PASSAGE MEANS BEING CONSTRUCTED TO PROVIDE A BYPASS PATHAROUND THE RESTRICTION DURING NON-BOILING OF THE WORKING LIQUID ANDPROVIDE A LIQUID SEAL FOR SAID BYPASS PATH DURING BOILING OF THE WORKINGLIQUID.